Kinetics and impacting factors of HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; uptake onto submicron atmospheric aerosols during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan

Jun Zhou,Yu Bai,Yasuhiro Sadanaga,Yosuke Sakamoto,Jiaru Li,Kentaro Murano,Sathiyamurthi Ramasamy,Nanase Kohno,Yoshizumi Kajii,Akinori Takami,Ayako Yoshino,Yoshihiro Nakashima,Kei Sato,Tomoki Nakayama,Yuka Kousa,Yukiko Fukusaki

doi:10.5194/acp-21-12243-2021

Abstract

Abstract. HO2 uptake kinetics onto ambient aerosols play pivotal roles in tropospheric chemistry but are not fully understood. Field measurements of aerosol chemical and physical properties should be linked to molecular-level kinetics; however, given that the HO2 reactivity of ambient aerosols is low, traditional analytical techniques are unable to achieve this goal. We developed an online approach to precisely investigate the lower-limit values of (i) the HO2 reactivities of ambient gases and aerosols and (ii) HO2 uptake coefficients onto ambient aerosols (γ) during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan. We identified the effects of individual chemical components of ambient aerosols on γ. The results were verified in laboratory studies on individual chemical components: transition metals play a key role in HO2 uptake processes, and chemical components indirectly influence such processes (i.e., by altering aerosol surface properties or providing active sites), with smaller particles tending to yield higher γ values than larger particles owing to the limitation of gas-phase diffusion being smaller with micrometer particles and the distribution of depleting species such as transition metal ions being mostly distributed in accumulation mode of aerosol. The modeling of γ utilized transition metal chemistry derived by previous studies, further confirming our conclusion. However, owing to the high NO concentrations in Yokohama, peroxy radical loss onto submicron aerosols has a negligible impact on O3 production rate and sensitivity regime.

Highlights

As an important atmospheric trace gas, the hydroperoxyl radical (HO2) links many of the key oxidants in the troposphere, including the hydroxyl radical (OH), nitrate radical (NO−3 ), ozone (O3), and hydrogen peroxide (H2O2)
This study used a reliable online methodology to investigate HO2 uptake kinetics onto in situ ambient aerosols (i.e., HO2 reactivity of ambient aerosols ka and HO2 uptake coefficients γ ) and discussed the impacting factors on such processes, i.e., chemical compositions and physical properties of ambient aerosols and experimental conditions. ka ranged between 0.001 s−1 (25th percentile) and 0.005 s−1 (75th percentile), with an average value of 0.005 ± 0.005 s−1
Zhou et al.: Kinetics and impacting factors of HO2 uptake onto submicron atmospheric aerosols dard deviation of the γ values along with the measurement time (± 0.21, 1σ ) may be due to the instantaneously changed chemical and physical properties of ambient aerosols; a large bias may exist if a constant γ value is used for modeling

Summary

Introduction

With γ > 0.1, HO2 concentration can be influenced under conditions such as low [NO] or high aerosol loading (Lakey et al, 2015; Mao et al., 2013b; Martínez et al, 2003; Tie et al, 2001; Jacob, 2000; Matthews et al, 2014). These effects make the HO2 uptake onto ambient aerosols indirectly influence human health and climate change

Methods

Results

Conclusion